(USATODAY.com) - It's a mystery in a world with few mysteries anymore.

Theories about what happened to Malaysia Airlines Flight 370 are rampant, though many are cobbled together with dubious clues or void of facts altogether. In the absence of concrete information on where the plane is, officials haven't ruled out any possible scenarios.

Here are some of the theories on what happened to the Beijing-bound flight that vanished early Saturday with 239 people aboard.

Catastrophicfailure

One experttoldUSA TODAY the lack of warnings about a problem aboard the aircraft suggests a catastrophic failure. Steve Marks, a partner at Podhurst Orseck law firm in Miami who has represented relatives of victims in airline crashes, said the Boeing 777 should have been relaying reports of problems - if there were any. A lack of reports could mean a catastrophic failure, perhaps from the plane breaking up.

Mechanical failure

The plane's transponder, which identifies it to civilian radar systems and other nearby planes, was not working. Experts say a massive failure knocking out its electrical systems, while unlikely, could also explain the outage.

Pilot sabotage

Another possibility on why the transponder was not working is that the pilot, or a passenger, likely one with some technical knowledge, switched them off in the hope of flying undetected.

Pilot error

Officials haven't ruled out pilot error, though information provided by Malaysia Airlines shows the crew in the cockpit were very experienced: The flight was piloted by Capt. Zaharie Ahmad Shah, 53, of Malaysia. He has 18,365 flying hours and joined the airlines in 1981. The first officer is listed as Fariq Abdul Hamid, 27, of Malaysia. He joined the airline in 2007 and has 2,763 total flight hours.

Terrorism

U.S. officials told USA TODAY over the weekend they were reviewing possible terror links. Terrorism theories were fueled by information that two Iranians who boarded the flight had stolen passports. Interpol Secretary-General Ronald Noble said neither man has a criminal record. The two had bought tickets to get to Europe, where they hoped to obtain asylum.

The plane kept flying

A U.S. official who spoke to the Associated Press on the condition of anonymity said Thursday investigators are beginning to explore whether the plane may have flown for another four hours after contact was lost, based on the estimated fuel onboard and the inability of searchers to find wreckage.